It is well known that excessive brush force applied against the teeth during brushing over an extended period of time is detrimental to oral health, causing wear of gum tissue and eventually the teeth enamel. This is true whether the brushing is accomplished manually or with a power toothbrush, although a power toothbrush may accentuate the effect. To avoid this, it is quite typical for a dental patient to receive instructions from the dental professional to use less pressure during brushing.
However, it is often quite difficult for an individual to self-monitor the pressure applied on the brush against the teeth and to maintain it within an acceptable range over the course of the brushing event. An acceptable range of pressure that is not injurious to the gums or teeth is known and has been verified experimentally. However, the typical toothbrush does not have a capability of measuring applied pressure and the tendency of individual users is to exert too much pressure against the teeth, particularly since a firm "scrubbing" action is usually regarded by the populace as being most effective for cleaning. As explained above, however, excessive or heavy scrubbing can lead to gum and even teeth damage.
In order to address and attempt to solve this issue of excessive pressure, pressure sensors of various types have been developed, although most are primarily for use with power toothbrushes, where the possibility of tissue and teeth damage is generally greater than for manual toothbrushes. Pressure sensors have been developed specifically for manual toothbrushes as well, however.
Known pressure sensors include various mechanical arrangements, including for example those shown in U.S. Pat. Nos. 5,146,645 and 5,355,544, both to Dirksing, which include a handle portion which deforms when excessive pressure is applied. Various kinds of electrical pressure sensing devices and/or direct pressure sensors have been used. Some examples of electrical-type pressure sensors include U.S. Pat. No. 4,450,599 to Scheller et al, U.S. Pat. No. 4,716,614 to Jones et al and U.S. Pat. No. 5,282,291 to Spieler et al. Still other examples include U.S. Pat. No. 5,784,742 and U.S. Pat. No. 5,815,872, both assigned to the assignee of the present invention.
In many of these devices, when a selective pressure threshold is reached, an electrical signal is produced, which is applied to an alarm mechanism. All of the above devices use an alarm of some kind, whether tactical, auditory or visual, to alert the user that the selected excessive pressure threshold has been exceeded. The user will then reduce the pressure being applied against the teeth until it goes below the pressure threshold, at which point the alarm ceases.
However, such previous pressure sensors typically are either quite expensive and/or complex, or in some cases are not reliable over an extended period of time. For a manual toothbrush, those pressure sensors which are in fact reliable in operation are often simply too expensive. A force or pressure sensor which is suitable for a manual toothbrush, such as that of the present invention, must be simple in structure and operation, must be reliable, and also must be economical. The total cost of the resulting manual toothbrush, including the pressure sensor system, must be reasonably competitive with other manual toothbrushes.